Gasoline is upgraded by improving, or raising, its octane number. The octane of a gasoline is its knock-resistance, which is a measure of the gasoline's resistance to autoignition. The autoignition causes the gasoline to prematurely combust and subsequently produces a knocking sound in an internal combustion engine. The knocking reduces the efficiency of the engine. The octane number is correlated with higher activation energies for a reaction to proceed, and therefore higher octane numbers have higher activation energies and a reduction in autoignition of a gasoline air mixture. Generally, gasoline is upgraded by reformulating the gasoline constituents by isomerization and aromatization. Gasoline is also upgraded by removing lower octane constituents from the mixture of hydrocarbons that make up gasoline. The lower octane constituents can be removed in several ways, but adsorptive separation provides an efficient method of selectively removing lower octane constituents from the mixture. This process technology is known as simulated moving bed process. The lower octane constituents are primarily smaller normal alkanes, such as normal pentane and normal hexane.
Improvements in the separation of light normal alkanes from gasoline can save equipment and energy costs.